Let-off motion in loom

ABSTRACT

A warp let-off mechanism for a loom having a warp beam driven through a variable speed transmission and a backrest over which the warp runs, the backrest being movable in a direction for increasing and decreasing warp tension and being resiliently urged against warp tension in the tension increasing direction, the variable speed transmission having means for varying the speed thereof. The warp let-off mechanism is comprised of a first adjustment means comprising backrest coupling means coupled between the backrest and the means for varying the speed of the variable speed transmission and responsive to an increase or decrease in tension in the warp as the removal of the warp from the warp beam progresses for adjusting the position of the varying means to increase or decrease, respectively, the speed of the warp beam for reducing or increasing, respectively, the tension. A second adjustment means is coupled to the first adjustment means and is responsive to adjusting movement of the first adjusting means for adjusting the coupling between the coupling means and the varying means to return the backrest to its initial position while maintaining the varying means in its adjusted position.

United States Patent Hosono et al.

[ Aug. 21, 1973 LET-OFF MOTION IN LOOM Primary Examiner-James Kee Chi[75] Inventors: Shinichi Hosono; Kazuyoshi Kida, Attorney-Mammoth Lmdand Ponack both of lshikawa-ken, Komatsu, Japan [57] ABSTRACT Assigneeili Limled, Osaka, Japan A warp let-ofi mechanism for a loom having awarp [22] Filed: Man 30 1970 beam driven through a variable speedtransmission and a backrest over which the warp runs, the backrest beingPP N05 23,684 movable in a direction for increasing and decreasing warptension and being resiliently urged against warp 52 US. Cl. 139/110tensim the increasing direcfim' the variable [51] Int. Cl D03d 49/06Speed transmission having means for varying the speed [58] Field ofSearch 139/110, 109, 99, Ihemf- The P mechanism is P of 3 139/115; 66/86A first adjustment means comprising backrest coupling means coupledbetween the backrest and the means for varying the speed of the variablespeed transmission [56] References Cited and responsive to an increaseor decrease in tension in UNITED STATES PATENTS the warp as the removalof the warp from the warp 2 435 437 N19 Foster at a] 139/110 beamprogresses for adjusting the position of the vary- 3:308:854 3/1967 i:139/99 ing means to increase or decrease, respectively, the 2,888,9556/1959 Kondo 139/99 Speed of the Warp beam for reducing or increasing,1,729,l30 9/1929 Seymour et a1... 139/110 spectively, the tension. Asecond adjustment means is 2,681,080 6/1954 Picanol 139/1 10 coupled tothe first adjustment means and is responsive 2,819,734 1/1958Pfarrwaller 139/110 (0 dj ting movement of the first adjusting means forFOREIGN PATENTS O APPLICATIONS adjusting the coupling between thecoupling means and the varying means to return the backrest to itsinitial fia i n position While maintaining the varying means in itsadjusted position.

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h INVENTORs Mil aka/1 M ATTORNEYS LET-OFF MOTION IN LOOM The presentinvention relates to let-off device in a loom wherein a warp beam and aback rest are jointly used.

A back rest has so far been in use in a loom to regulate warp tension.The back rest is displaced according to warp tension variations toalleviate them. The normal position of the back rest is point at whichwarp tension is regular. A spring or a counter weight is attached to theback rest and consequently the back rest is not stationary but movable.When warp tension increases, the back rest is assumed to be displaced inthe direction 0 M and when it decreases, it is assumed to be displacedin the direction 0 M and when it decreases, it is assumed to bedisplaced in the direction 0 L. The back rest can move back and forth online The causes of changes in warp tension are two-fold. A first causeis nonuniformity of warp package building or nonuniformity of the courseof weaving. A second cause is that the winding diameter of a warp beamgradually becomes smaller. The first cause is mostly temporary; forinstance, warp tension fluctuates temporarily owing to non-uniformity ofthe course of weaving. In the case of increase in warp tension, the backrest moves in the direction 0 M to alleviate instantly an increase inwarp tension. In contrast, when warp tension decreases, the back restmoves in the direction 0 L to alleviate instantly decreases in warptension. With respect to the first cause, the back rest moves by itselfin response to the increase or decrease of warp tension to regulate it.Hence when warp tension variations occur only due to the first cause,the back rest moves back and forth in the direction 0 M or O L as thecase may be. i

As a matter of fact the second cause inevitably combines with the firstcause to cause a greater movement of the back rest.

As described before, the winding diameter of the warp package graduallydecreases with the progress of weaving. If the rotation of a warp beamis constant (in fact, constant rotation of a warp beam is the prevailingpractice), the consumption of warp yarn on the weaving side isconstant,.and the shortage of warp supply appears first as an increaseof warp tension. This phenomenon is inevitable and continuous. Whenthere are no counter-measures against warp tension variations, the

back rest is continuously pushed in the direction C) M and let-offmotion will come to a standstill. One countermeasure has been thedisplacement of the back rest used to control the rotation of the warpbeam. The above-mentioned two types of causes combine to generate warptension variations and the back rest is caused to respond to thegenerated warp tension variations. The displacement of the back rest isthen transmitted to a variable speed transmission, which is connectedwith the shaft of the warp beam. Thus the number of rotations of thewarp beam is controlled by the displacement of the back rest responsiveto the tension variations of warp yarn via a connecting member or avariable speed transmission to keep warp tension normal.

In short, the back rest displaces itself in response to warp tensionvariations and serves as an alleviator of tension variations and withthe use of the displacement, the back rest controls the number ofrotations of the 2 warp beam and keeps the warp tension at normalconditions.

Such a technological idea is well known in the art and variousimprovements or devices have so far been provided.

The present invention relates to such improvements in the art.

A conventional back rest is usually provided with a spring or a counterweight such that it is balanced with warp tension. It is found, however,that the counter weight is not satisfactory because it is difficult forthe weight to follow vibrations due to the high pitch of warp tensiondue to high speed weaving.

Although a spring acts more favorably than a counter weight, it hasstill a drawback. One end of the spring is secured to the frame and theother to a lever. The lever extends in a direction opposite to thespring via a pivot, and on the other end of the lever is mounted theback rest. The spring applies to the back rest a bearing force to causeit to be well-balanced with the warp tension. As described before, asthe diameter of the warp package decreases, the back rest moves frompoint 0 toward point M.

The displacement progressively increases, and the back rest will notreturn to point 0. If the back rest has moved to point M the bearingforce applied to the back rest by the spring at this time could begreater than that at point 0. With the progressive displacement of theback rest from point 0 to point M, the bearing force graduallyincreases, resulting in the increase of warp tension. This drawback isalways present as long as the back rest is provided with a spring. Inorder that the drawback may be minimal, it is essential that the length0 M be appropriately small and that when the back rest reaches point M,it can automatically return to point 0.

The above-described improvement is also necessary for another reason. Inthe special case of a back rest which uses a spring as well as ingeneral cases, the total length which the back rest moves from a fullwarp beam to an empty warp beam depends on the winding diameter of thewarp package. When the winding diameter of the warp package is small,the length of displacement is comparatively small. However with therecent trend to a larger warp package, the length of displacement of theback rest becomes great, and it has to be returned to point 0frequently. It is troublesome to manually return the back rest to thenormal point frequently and automation is thus required.

After long research on this point, the inventors have come to thefollowing conclusion.

When the back rest is displaced to point M on account of warp tensionvariations, the temporary loosening of warp tension will suffice. Atthat time the back rest will immediately return in the direction M 0,because the spring is working on the back rest. And if the warp tensionacting on the back rest which has returned to point 0 can be kept as inthe normal condition, the desired object ought to be attained.

For this reason, the inventors have carefully studied various means ofloosening warp tension and finally found,that it is very effective toalter the length of connecting means between the back rest and thetransmission lever.

An inevitable drawback due to the fact that the length of the connectingmeans is constant in conventional back rests will be described below.

In order to compensate for a decrease in the diameter of the warppackage, which occurs without fail due to the above-described secondcause, it is necessary to continue to increase the warp beam rotatingspeed. In doing so, the transmission lever should be kept on increasingspeed. That is, in keeping the amount of let off constant, thetransmission lever always should be displaced in a direction of speedincrease. Hence when the back rest is connected with the transmissionlever with connecting means of constant length, the back rest has to bekept on being displaced in the O M direction according to theprogressive displacement of the transmission lever. The progressivedisplacement of the back rest causes an increase in warp tension by theaction of a spring. As long as the length of means for connecting theback rest with the transmission lever is kept constant, weaving iscompelled to proceed with progressively increasing warp tensionresponsive to the gradual decrease of the diameter of the warp beam.This is a very undesirable drawback.

In the present invention, the displacement of the back rest istransmitted to a speed transmission via a lever to control the rotationof the warp beam. Hereinafter this adjustment is referred to as a firstadjustment and the subsequent adjustment as a second adjustment. Thesecond adjustment occurs when the back rest comes to point M, therotation of the warp beam is temporarily increased to lower warptension. As a result the back rest automatically returns to its normalposition 0. By the second adjustment (later discussed in detail), thewarp tension is restored to its normal condition.

At the end of the first adjustment, the back rest reaches point M; thelever, the shaft, etc., connected to the back rest and to each othermove in each direction, and as these connecting means arenonretractable, they move as a whole in a series relationship. The sumof the lengths of each portion extending up to the joint (connectingpoint of the transmission lever), which is the end of the connectingmeans with the cardinal point at the back rest is constant. However inthe second adjustment of the present invention, lengths of connectingmeans are supplemented in the neighborhood of the joint to increase therotation of the transmission lever. in short, in the present invention,the tip of the connecting means advanced in the first adjustment iscaused to advance farther to restore the position of the back rest andregain the normal warp tension.

As described above, it is most essential to return the back rest to itsnormal position, and the conventional methods have thus been improved.

The present invention comprises a yarn tension device to adjust therotation of the warp beam by making use of the displacement of a backrest and means to restore the displaced back rest to its normalposition, and it is the object of this invention to effectively combinethese means and to maintain a constant warp tension regardless of thediameter of the warp package wound on the warp beam for producing goodfabric.

One embodiment will be described below with reference to theaccompanying drawings.

FIG. 1 is a front view illustrating one embodiment of the presentinvention.

FIG. 2 is an enlarged view of a control assembly shown in FIG. 1.

FIG. 3 is a cross sectional view on line A-B of FIG. 2.

FIG. 4 is a front view of a modified rotational device. FIG. 5 is agraph showing the relation between the displacement of a speed back restand let-off.

FIG. 6 is a graph showing variations in the rate of let- 5 off in thedisplacement restoration of a back rest.

Referring to FIG. 1 a warp beam 10 and back rest 12 are mounted on loomframe 1. Warp threads W wound on warp beam 10 are led to the loom bypassing over the periphery of back rest 12. It is well known that a backrest is used for governing tension control motion, that the rotation ofa warp beam is controlled to govern warp tension and that the rotationof the warp beam is governed by utilizing the displacement of a backrest. In such tension device, backrest 12 is rotatably mounted on theend of rod 13. Rod 13 is rotatably connected to the end of L-shapedlever having shaft 14 as its fulcrum. Spring S is secured to L-shapedlever 15 halfway between its free end and its fulcrum 14. The other endof spring S is secured to loom frame 1. To the free end of lever 15 isattached rod 16 by means of bracket 17. The up-and-down motions of rod16 are prevented with collar 18 mounted to bracket 17. To the lower endof rod 16 is attached threaded shaft 21 by means of universal joint 20.The other end of threaded shaft 21 is held in supporting metal arms 22and 22 mounted on frame 1. Joint 34is threaded on threaded shaft 21 andretractably connected to variable speed transmission 4 by means oftransmission lever 33 on transmission speed ratio adjusting shaft 33'.The rod 13, lever 15, rod 16, shaft 21 and joint 34 arefirst adjustingmeans. The variable speed transmission can be a conventional V-pulleydisc type, cone pulley type or one having a similar function. The oneshown in FIG. 1 is a type in which a transmission is disposed in a boxand has an input and an output shaft, and by rotating the shaft 33, thespeed ratio is adjusted. Now, power is received at the input shaft (notshown) of variable speed transmission 4 through rotary chain 3, etc.from rotary shaft 2 and is speed varied by variable speed transmission4. Warp beam 10 is rotated by means of output shaft 5, gear 5' on theshaft 5, gear 7 on the other transmission shaft 6, a set of bevel gears(not shown) on shaft 6 and the other shaft 8, worm 9 on shaft 8, andgear 11 on the shaft of warp beam 10. The train of elements from gear5"to gear 11 is referred to as the rotational means for the warp beam.

With such mechanism, back rest 12 moves with changes in warp tension.That is, when tension is high, back rest 12 moves in the direction toreduce tension, the direction 0 M, and stops moving at a point ofdisplacement where the balance of force between it and spring S attachedto L-shaped lever 15 connected to back rest 12 is attained. The obliqueforce of spring S bears always on back rest 12 and keeps in balance withthe warp tension. Thus, as the position of the back rest changes betweenM-O-L, the force of the spring bearing on the back rest varies andsubsequently warp tension varies too. As previously described, such is adrawback of the conventional control system.

In order that the above-mentioned function may be understood moreclearly, an embodiment will be described below with reference to FIG. 5.In FIG. 5 the time elapsed is plotted as the abscissa, and let-off speedas the upper ordinate. Let standard let-off speed be a. a is illustratedin plus and minus percentage above and below said standard line (a). Asthe lower ordinate there is plotted the position of the back rest. Above0,

the central position of the back rest, is given L and below 0 is given 0M. At the time of start-up, let-off speed is on I, that is, standardline a, back rest 12 on a, that is, O. The let-off speed (3) of warpthreads gradually falls and reaches II as time goes on. The back restmoves toward M and reaches b. By the displacement of a b, threaded shaft21 is pushed downward, and let-off speed (B) of the warp beam increasesby the rotational means of transmission 4, etc., through joint 34 andtransmission lever 33 to correspond to standard let-off speed (a). Thatis, speed (B) changes form (II) (III), during which time the back restoccupies a position of displacement which does not change (b 0).However, the let-off speed of warp threads which have returned tostandard speed (a) continues to decrease afterwards [(III) (lV)]. Againthe backrest moves to decrease warp tension (0 d), and thereafter thesame as above, the yarn speed is controlled to change IV V while thebackrest remains in position (d e); again as yarn speed (B) changes V VIand VI VII, the back rest moves e f and f 1:. As the back rest changesits position between 0 and M, the bearing force of the back rest on thewarp varies at each position of displacement, because this bearing forceoriginates from spring S. As described above, by the first control, yarnspeed (/3) is adjusted, but the bearing force on the warp producing warptension varies.

When back rest 12 moves toward M with increase in warp tension, the freeend of L-shaped lever pivoted at shaft 14 rotates downwards and threadedshaft 21 moves down. Consequently joint 34 threaded on threaded shaft 21moves down to cause shaft 33 of transmission 4 to rotate throughtransmission lever 33. The interior of the transmission is actuated bythe rotation of shaft 33' to accelerate the rotation of shaft 5. Whenjoint 34 moves upward, the transmission direction is reversed todecelerate shaft 5. As described above, when the back rest is displaced,transmission lever 33 is caused to rotate directly correspondingly tothe displacement of the back rest to decelerate or accelerate warp beam10 for regulating the rate of let-off on the loom. At this time, theback rest is stationed at a point of displacement. Such means requiredfor this function from rod 13, lever 15, rod 16, threaded shaft 21, andjoint 34 to transmission lever 33 is referred to as the tension device.Any means may be used if the displacement of back rest 12 can beconverted into that of transmission lever 33. The mechanism of thetransmission is also optional. Such is the summary of the firstregulation.

In such a warp tension device back rest 12 cannot return to its originalposition. In the present invention the return of back rest 12 to itsnormal position can be accomplished by various second adjustment means.A specific device will be described below.

In FIGS. 1, 2 and 3, the lower end of threaded shaft 21 runs throughsupporting metal arms 22 and 22', and halfway between the arms, ratchetwheels 27 and 28 are secured to threaded shaft 21, with a space Gbetween them and with the direction of teeth of the ratchet wheelsopposite to each other. The teeth of either said ratchet wheels can beactuated by an outside force to cause threaded shaft 21 to rotate. Theoutside force is applied by a U-shaped lever 19 comprising two legs 23and 24 pivoted on shaft 21, ratchets 25 and 26 pivotally attached to themiddle point of a connecting member connecting said legs, arm 30extending from the connecting member in a direction opposite to thedirection said ratchets and legs extend and a cam ball 31 at the end ofsaid arm 30. Said lever 19 is rotatably mounted on threaded shaft 21 sothat it can rotate with shaft 21 with the center at the shaft when thecam ball 17 is oscillated. As a means of oscillating cam ball 31 camwheel 32 is provided in front of gear 7 and is attached to intermediateshaft 6 driving the warp beam. The cam wheel is circular and has aninclined annular cam surface thereon. When the annular cam surfacerotates, cam ball 31 in contact with the wheel is subjected tooscillations back and forth while being guided by the cam surface. Thuscam ball 31 makes reciprocating, arcuate motions together with lever 19,with the center at shaft 21. This is, cam ball 31, while sliding alongthe surface of cam wheel 32 makes reciprocating motions perpendicular tothe surface of the cam wheel to permit lever 19 connected to said camball 31 to make reciprocating, arcuate motions with the center at screwshaft 21. In such mechanism, if either of ratchets 25 and 26 engageseither of ratchet wheels 27 and 28, it causes the ratchet wheel torotate in a predetermined rotational direction and accordingly shaft 21rotates. As shown in FIG. 2, when ratchets 25 and 26 are positioned inspace G, the rotation of shaft 21 does not take place. When shaft 21makes up-and-down motions, the ratchets begin engaging the ratchetwheels. For instance, when shaft 21 descends, ratchets 25 and 26 meshwith ratchet wheel 27, and shaft 21 rotates in a predetermineddirection.

When shaft 21 descends, the ratchets are engaged with ratchet wheel 28and the shaft rotates in the oppo site direction. When the ratchets meshwith the upper wheel 27 for rotating the shaft, the direction ofrotation is such that joint 34 is threaded down the shaft andtransmission lever 33 is pushed down, and when the lever wheel 28 mesheswith the ratchets, the direction of rotation is such that transmissionlever 33 is pushed up in the reverse manner. The above is the secondadjustment, the most essential part, in the present invention. 7

Now the relationships between the first and second adjustments will bedescribed below.

At the start of the weaving operations, the back rest is positioned at Oand ratchets 25 and 26 are arranged to be located in space G. Handle His manually manipulated so that the warp beam is in good order, andjoint 34 is moved to a predetermined position for starting the loom.

During the weaving, when warp tension is too high, back rest 12 iscaused to move in the direction to reduce tension (0 M). The free end ofL-shaped lever 15 is rotated in the counterclockwise direction to pushdown rod 16 and threaded shaft 21 connected thereto. As joint 34 isthreaded on threaded shaft 21, it descends together with the shaft andcauses shaft 33' of variable speed transmission 4 to rotate. This actionpermits the warp beam to accelerate via rotary means of the warp beam.Accordingly warp tension is reduced to a desirable tension.

Nevertheless back rest 12 remains displaced. Such is the firstadjustment, but at this time the second adjustment has already begun. Asseen in FIGS. 1 and 2, during the first adjustment threaded shaft 21descends. Prior to this time lever 19 and ratchets 25 and 26 arepositioned as shown in the Figs. But ratchet wheels 27 and 28 secured toshaft 21 descend together with shaft 21 to make ratchets 25 and 26engage ratchet wheel 27. Thus the second adjustment begins to follow thefirst adjustment slowly. That is, the ratchets of lever 19 make shaft 21slowly rotate through the ratchet wheel 27 to gradually push down joint34.

Threaded shaft 21 has moved downward in the first adjustment andaccelerated the rotation of the warp beam. Successively to this control,the second adjustment makes joint 34 descend and the warp beam furtheraccelerates. Warp tension thus becomes lower. Taking advantage of thislow tension, back rest 21 starts moving from M to O, by means of theforce of spring S, secured to L-shaped lever 15. The spring returns backrest 12 to position 0, rotates clockwise the free end of L-shaped lever15 to pull up rod 16 and shaft 21. Ratchet wheel 27 is thereby pulled upand released from between the ratchets, and ratchets and 26 are returnedto space G. As described above, when shaft 21 is pulled up and returnedto the position of the first adjustment, this results in the removal ofthe second adjustment; consequently, warp beam 10 and warp tensionreturn to the state of the beginning of the first adjustment, and backrest 12 occupies O. This displacement is most desirable. Such is anexample of too high warp tension, and in the case of too low warptension, the second adjustment follows the first adjustment and afterthe restoration of back rest 12 the second adjustment is removed withthe exception that the movements of levers, etc. is opposite to those inthe case of high warp tension.

Said second adjustment is the essential part of this invention, alwaysfollowing the first adjustment and the main object is to permit backrest 12 displaced in the first adjustment to return to position 0. Themeans required for this object, that is, cam ball 31, cam 32, arm 30,lever 19, ratchets 25, 26, ratchet wheels 27 and 28, threaded shaft 21,transmission lever 33, etc. (shown in the drawings) are the rotaryassembly for back rest restoration.

Another modified embodiment is shown in FIG. 4. Bevel gear 43 is rotatedby pulley 38 attached to shaft 6 of gear 11 and belt 41. In a verticalplane meeting at right angles with shaft 42 of said bevel gear 43 isthreaded shaft 21 to which upper bevel gear 44 and lower bevel gear 45are secured at appropriate intervals. When threaded shaft 21 descends,upper bevel gear 44 meshes with bevel gear 43 positioned in the centerto cause shaft 21 to rotate in the direction of arrow X, and when shaft21 ascends, lower gear 45 meshes with bevel gear 43 in the center tocause shaft 21 to rotate in the opposite direction, that is, thedirection of arrow Y. Together with the rotation of shaft 21, asdescribed above, joint 34 threaded on threaded shaft 21 moves up anddown to control the warp beam.

Restoration means for the back rest is not limited to the embodimentsshown in the drawings, and any means whereby the back rest which hasbeen displaced so that the supply and demand of warp threads arebalanced is returned to its original position while warp tension isbeing maintained as desired and whereby the threaded shaft is caused torotate in the restoration direction only when the back rest is itsnormal position, may be employed.

In the present invention, the position of joint 34 threaded on shaft 21moves at every adjustment and the range of its movement canexperimentally be determined beforehand. Hence, the length correspondingto the range may be given to threaded shaft 21. Further the movement ofjoint 34 is possible by the manual rotation of shaft 21. Such is anexplanation of one working example. Other working examples follow:

EXAMPLE I In FIG. 1, after the first adjustment has occurred by thedisplacement of back rest 12, threaded shaft 21 is caused to rotate in agiven direction to generate the second adjustment. This shaft may berotated by a different power source. In order that the displacement maybe transmitted to said power source, an electric switch or aphotoelectric cell in an electric circuit is set in the back rest 12system to carry out the on-off control for the circuit, by making use ofthe displacement of back rest 12.

EXAMPLE 2 When an electric switch or a photoelectric cell is set in backrest system in Example I, a magnet or an electric rotator may be set inthe circuit to promote the speed control of transmission 4 additionally.In this case shaped lever 19 is not in use. Hence a nonscrewed bar inplace of screw shaft 21 may be used.

EXAMPLE 3 A hydraulic cylinder is attached to any of back rest 12, rod13 connected thereto, and lever 15 to introduce pressure liquidgenerated in the hydraulic cylinder by making use of the displacement ofsaid back rest 12 system into the main part of transmission 4 through aconduit for adjusting the speed of said transmission 4.

In order that the function of the present invention may be more fullyunderstood, referring to the graph in FIG. 6, the relation between thefirst and second adjustments for the amount of let-off will be explainedbelow. The upper diagram shows the displacement of the back rest and thelower diagram said displacement vs. the amount of let-off. The time ofprogress is plotted as the abscissa and the displacementiof the backrest (upper diagram) and the amount of warp let-off (lower diagram) asordinates.

When the back rest is displaced in O M, then M 0, the first adjustmenttakes place mainly between 0 and M and the amount of let-off ismaintained at a standard amount (Vn), whereas mainly the secondadjustment takes place and the standard amount of let-off (Vn) is keptbetween M and O. In short, the warp is maintained at the standard amountof let-off (Vn) through the whole course. The state in 0 M is firstdescribed.

When the back rest is positioned at point 0, the diameter of warppackage wound on the warp beam is in an appropriate size, and so theamount of let-off (V, unwound from the constantly rotating warp beamagrees with standard amount of let-ofi- (Vn). However as time goes on,warp threads are consumed, and the diameter of the warp packagedecreases. Therefore the amount of let-off (V, unwound from theconstantly rotating warp beam decreases as shown in the diagram andbecomes insufficient compared to the standard amount.

In order that this shortage may be made up for, amount of let-off (Vcaused bythe acceleration of the warp beam due to the displacement ofthe back rest and the transmission lever and amount of let-off (V causedby decrease of the length of the warp from the warp beam to the clothfell due to the displacement of the back rest are added to said amount(V As a result, in this stage the amount of let-off is maintained at thestandard amount of let-off (Vn). Then when the back rest reaches R thesecond adjustment starts. For instance, in examples 1 and 2, theadditional displacement of the transmission lever begins on account ofthe rotation of the threaded shaft. And in example 3, the electriccircuit turns on and magnet, etc. start additional adjustment. Theabove-mentioned adjustment is continued until the back rest is displacedto R the same phrase as R,. The amount of let-off (V, turns into (V,exceeding the standard amount (Vn), and excessive warp is let-off toloosen warp tension. Through the looseness of the warp tension, the backrest is displaced in a direction of (O n M), reaching R and by stoppingthe rotation of the screw shaft and by the electric circuit being off,the warp beam is slightly adjusted in the deceleration direction. Evenat this point, the warp beam is rotating in overfeed. And even if itrotates at equal speeds afterwards, the amount of let-off (V decreasesas shown in the diagram on account of decrease in the diameter of thewarp package and the surplus over standard amount of let-off (Vn)continues to decrease as time goes on. Negative amount of let-off (Vgenerated by the deceleration of the warp beam due to the displacementof the back rest and the transmission lever and negative amount oflet-off (V generated by increase of the length of warp between the warpbeam and the cloth fell due to the displacement of the back rest arededucted from the amount of let-off (V As a result, even in this stage,the amount of let-off is maintained at the standard amount of let-off(Vn).

Further, in the present invention, the back rest is not only restored tothe normal position under the standard amount of let-off but also thevelocity of restoration is appropriately slow and freely adjustable.That is, if the oscillation length and number of rotations of ratchets25 and 26, the number of teeth of ratchet wheels 27 and 28, etc. areproperly adjusted, the restoration velocity of the back rest M O or L atO can be such that the degradation of appearance and quality of fabricdue to warp tension variations at the time of restoration is a minimum.As described above, since when the back rest is displaced, it isaccurately restored to the normal position at a predetermined slow speedwhile the actual warp tension is being maintained as near the standardconditions as possible, warp tension can be maintained in the nonnalstate throughout the weaving operation.

We claim:

1. in a loom having a warp beam driven through a variable speedtransmission and a backrest over which the warp runs, the backrest beingmovable in a direction for increasing and decreasing warp tension andbeing resiliently urged against warp tension in the tension increasingdirection, the variable speed transmission having means for varying thespeed thereof. a warp let-off mechanism comprised of a first adjustmentmeans comprising backrest coupling means coupled between said backrestand said means for varying the speed of said variable speed transmissionand responsive to an increase or decrease in tension in the warp as theremoval of the warp from the warp beam progresses for adjusting theposition of said varying means to increase or decrease, respectively,the speed of the warp beam for reducing or increasing, respectively, thetension, and a second adjustment means coupled to said first adjustmentmeans and responsive to adjusting movement of said first adjusting meansfor adjusting the coupling between said coupling means and said varyingmeans to return the backrest to its initial posi tion while maintainingsaid varying means in its adjusted position.

2. In a loom having a warp beam driven through a variable speedtransmission and a backrest over which the warp runs, the backrest beingmovable in a direction for increasing and decreasing the warp tensionand being resiliently urged against warp tension in the tensionincreasing direction, the variable speed transmission having a lever forvarying the speed thereof, a warp let-off mechanism comprised of a firstadjustment means comprising a lever and rod means and a threaded shaftcoupled to the backrest and a joint on said threaded shaft connected tosaid variable speed transmission lever, the variable speed transmissionlever being movedto an adjusted position to increase or decrease thespeed of the warp beam for reducing or increasing, respectfully, thewarp tension in response to an increase or decrease, respectively, ofwarp tension as the removal of the warp from the warp beam progresses,and a second adjustment means comprising a shaft rotating meanspositioned adjacent said threaded shaft and coupled to said threadedshaft only when said threaded shaft moves in response to changed warptension, and driving means coupled to said shaft rotating means fordriving said shaft rotating means, said shaft rotating means rotatingsaid threaded shaft in a direction to move said shaft relative to saidjoint to return the backrest to its initial position while maintainingsaid joint and said transmission lever at the adjusted position.

3. A warp let-off mechanism as claimed in claim 2 in which said secondadjustment means comprises ratchet wheel means on said threaded shaftand ratchet means positioned adjacent said shaft and spaced from saidratchet wheel means when the backrest is in the normal position andengaged with said ratchet wheel means when said backrest is displacedfrom the normal position due to a change in the warp tension.

4. A warp let-off mechanism as claimed in claim 3 in which said drivingmeans coupled to said shaft rotating means comprises a lever means onwhich said ratchet means is mounted, and cam means driven by saidtransmission engaged with said lever means for oscillating said levermeans.

5. A warp let-off mechanism as claimed in claim 2 in which said secondadjustment means comprises bevel gear means on said threaded shaft andfurther bevel gear means positioned adjacent said shaft and spaced fromsaid firstmentioned bevel gear means when the backrest is in the nonnalposition and engaged with said firstmentioned bevel gear means when saidbackrest is displaced from the normal position due to a change in thewarp tension.

6. A warp let-off mechanism as claimed in claim 5 in which said drivingmeans coupled to said shaft rotating means comprises a drive shaftcoupled to said further bevel gear and driven by said transmission.

i i l l i

1. In a loom having a warp beam driven through a variable speedtransmission and a backrest over which the warp runs, the backrest beingmovable in a direction for increasing and decreasing warp tension andbeing resiliently urged against warp tension in the tension increasingdirection, the variable speed transmission having means for varying thespeed thereof, a warp let-off mechanism comprised of a first adjustmentmeans comprising backrest coupling means coupled between said backrestand said means for varying the speed of said variable speed transmissionand responsive to an increase or decrease in tension in the warp as theremoval of the warp from the warp beam progresses for adjusting theposition of said varying means to increase or decrease, respectively,the speed of the warp beam for reducing or increasing, respectively, thetension, and a second adjustment means coupled to said first adjustmentmeans and responsive to adjusting movement of said first adjusting meansfor adjusting the coupling between said coupling means and said varyingmeans to return the backrest to its initial position while maintainingsaid varying means in its adjusted position.
 2. In a loom having a warpbeam driven through a variable speed transmission and a backrest overwhich the warp runs, the backrest being movable in a direction forincreasing and decreasing the warp tension and being resiliently urgedagainst warp tension in the tension increasing direction, the variablespeed transmission having a lever for varying the speed thereof, a warplet-off mechanism comprised of a first adjustment means comprising alever and rod means and a threaded shaft coupled to the backrest and ajoint on said threaded shaft connected to said variable speedtransmission lever, the variable speed transmission lever being moved toan adjusted position to increase or decrease the speed of the warp beamfor reducing or increasing, respectfully, the warp tension in responseto an increase or decrease, respectively, of warp tension as the removalof the warp from the warp beam progresses, and a second adjustment meanscomprising a shaft rotating means positioned adjacent said threadedshaft and coupled to said threaded shaft only when said threaded shaftmoves in response to changed warp tension, and driving means coupled tosaid shaft rotating means for driving said shaft rotating means, saidshaft rotating means rotating said threaded shaft in a direction to movesaid shaft relative to said joint to return the backrest to its initialposition while maintaining said joint and said transmission lever at theadjusted position.
 3. A warp let-off mechanism as claimed in claim 2 inwhich said second adjustment means comprises ratchet wheel means on saidthreaded shaft and ratchet means positioned adjacent said shaft andspaced from said ratchet wheel means when the backrest is in the normalposition and engaged with said ratchet wheel means when said backrest isdisplaced from the normal position due to a change in the warp tension.4. A warp let-off mechanism as claimed in claim 3 in which said drivingmeans coupled to said shaft rotating means comprises a lever means onwhich said ratchet means is mounted, and cam means driven by saidtransmission engaged with said lever means for oscillating said levermeans.
 5. A warp let-off mechanism as claimed in claim 2 in which saidsecond adjustment means comprises bevel gear means on said threadedshaft and further bevel gear means positioned adjacent said shaft andspaced from said firstmentioned bevel gear means when the backrest is inthe normal position and engaged with said firstmentioned bevel gearmeans when said backrest is displaced from the normal position due to achange in the warp tension.
 6. A warp let-off mechanism as claimed inclaim 5 in which said driving means coupled to said shaft rotating meanscomprises a drive shaft coupled to said further bevel gear and driven bysaid transmission.